1. Technical Field
This application relates to UMTS (Universal Mobile Telecommunications System) in general, and to an apparatus and method for determining uplink ciphering activation time in universal mobile telecommunications system user equipment in particular.
2. Description of the Related Art
UMTS is a third generation public land mobile telecommunication system. Various standardization bodies are known to publish and set standards for UMTS, each in their respective areas of competence. For instance, the 3GPP (Third Generation Partnership Project) has been known to publish and set standards for GSM (Global System for Mobile Communications) based UMTS and the 3GPP2 (Third Generation Partnership Project 2) has been known to publish and set standards for CDMA (Code Division Multiple Access) based UMTS. Within the scope of a particular standardization body, specific partners publish and set standards in their respective areas.
In UMTS, the data flow on any connection, known as a radio bearer, between a user equipment (UE) and the UMTS Terrestrial Radio Access Network (UTRAN) can be ciphered i.e. encrypted at any point in time, under the control of commands from the UTRAN. The ciphering start or activation time is the logical sequence number at which the UE and UTRAN both change the ciphering configuration used on that radio bearer in a given direction, either uplink or downlink. This ensures synchronicity between the UE and UTRAN and facilitates a smooth ciphering changeover without undue delay. A separate time-independent logical sequence number is maintained for each radio bearer for each direction. It increments by one for every packet transferred between the UE and UTRAN.
In the 3GPP technical specification for the UE control process (3GPP TS 25.331 v3.13.0. RRC protocol specification), section 8.6.3.4 states that if a new ciphering configuration is to be applied and there is no pending ciphering activation time, from a previous ciphering change, then the UE is to choose an activation time for the new ciphering configuration to be applied. However, the specification does not give a method for choosing the activation time. The only guidance it gives is to “set a suitable value that would ensure a minimised delay in the change to the latest ciphering configuration”. This guidance is open to substantial interpretation as to how a suitable value should be chosen.
The present invention aims to address the above problem.